Control circuits for gas filled cold cathode tubes



May 27, 1958 B. BRIGHTMAN 2,836,765

CONTROL CIRCUITS FOR GAS FILLED cow. CATHODE TUBES Filed Feb. 20, 1956 Invemor BARRIE BRIGHT/WAN Attorneys CONTROL CIRCUITS FOR GAS FILLED COLD CATHODE TUBES Barrie Brightman, Liverpool, England, assignor to Automatic Telephone & Electric Company Limited, Liverpool, England Application February 20, 1956, Serial No. 566,641 Claims priority, application Great Britain March 11, 1955 2 Claims. (Cl. 315-845) The present invention relates to electrical circuit arrangements and is particularly concerned with control circuits for gas-filled cold-cathode tubes.

It is often required to extinguish a large number of cold-cathode tubes simultaneously and for this purpose it is usual to insert a controlling means in the common high tension supply path to the anodes. A relay contact may be used but its relatively slow-operating speed is disadvantageous in some circumstances. Alternatively the necessary control may be obtained from a cathode follower, but to produce the requisite value of switched H. T. for the cold cathode tubes, a much higher voltage must be supplied to the cathode follower. The provision of the latter supply may be relatively costly and the high power consumption of the cathode follower is undesirable.

The cathode follower method of deriving switched H. T. anode supply is not entirely satisfactory in those circuits which require nominally simultaneous firing of a plurality of cold-cathode tubes served by the supply. In circuits of this type although the tubes may be supplied from a common pulse-firing source they do not have precisely the same firing times, and accordingly the tubes which fire firsttend to lower the effective H. T. thereby preventing the other tubes from firing.

The object of the present invention is to provide a control circuit which enables simultaneous extinguishing of a plurality of tubes to take place and at the same time also enables a plurality of tubes to be fired simultaneously.

According to the invention, in circuit arrangements for enabling the simultaneous firing and simultaneous extinction of a plurality of cold-cathode tubes, a thermionic tube arranged to be switched on and off is provided and a switched high tension supply for said tubes derived from the anode load resistor of said thermionic tube is applied to the anodes of the gas discharge tubes through V incorporating gas-filled cold-cathode triode tubes VKPRl and VKPRn respectively are typical of what may be a large number of similar stages. Information to be transferred is indicated by the presence or absence of positive potentials on leads M1 to Mn of the various stages, and each stage has an output pulse lead 0P1 to OPn. The thermionic pentode tube VD is concerned with the provision of switched H. T. to the transfer tubes whereas the cold-cathode triode tube VKPT is concerned with the initiation of the transfer of information.

In the quiescent state of the circuit, tube VD is nonconducting and'accordingly a capacitor such as C1, in each transfer stage, which is connected to earth over a resistor Rl, is charged 13-0 volts cf the high-ton Lllu ice

2 sion supply. Leads M1 to Mn have positive marking potentialsapplied .to them as circumstances require for a particular item of information, and these potentials extending over resistors such as R4 to the trigger electrodes of the relevant transfer tubes serve to bias the latter.

A demand for the transfer of the information takes the of a positive pulse received over lead TDL and this pulse results in the firing of the permanently primed cold-cathode tube VKPT. Thereupon the potential at the anode becomes less positive, so that a negative pulse is extended to the cathodes of all the transfer tubes VKPRI to VKPRn. The negative pulses bring about conduction of thosetransfer tubes which were previously biased, by increasing the voltage across the trigger/cathode gaps, and it is important to note that for the purpose of firing the tubes the charged capacitors such as C1 provide what is virtually an independent H. T. anode supply for each tube due to the fact that the resistor R2 has a greater value than R1 (e. g. 10 times). The possibility of failure in firing a relatively slow tube due to reduction of the H. T. by the common supply lead resistor R20 is obviated.

Consequent upon the firing of the primed transfer tubes a negative pulse is generated at the corresponding ones of output leads CPI and OPn and so the necessary transfer of information is accomplished.

When it is required to extinguish the fired transfer tubes, a positive pulse is appliedto lead DL to render the thermionic tube VD conducting and thereupon a considerable voltage drop is produced across the common anode resistor RZil. Consequently the voltage across the main gap of the transfer tubes is reduced to a value which will not support conduction so that the fired transfer tubes are extinguished.

In the particular embodiment of the invention the cold-cathode tubes are of the Hivac type XCll, the thermionic tube VD is type EL91 and it may be mentioned that suitable values for capacitor C1 and resistors R1, R2, R3 and R20 are 0.01 mf., 22K, 220K, 33K and 5K respectively.

In the typical circuit the tube VKPT would remain fired once it has been so conditioned but it will be understood that the tube could quite readily be arranged to be self-extinguishing. Alternatively it could be eX- tinguished by connecting its anode resistor to a source of switched H. T., for instance it might even be connected to the lower end of resistor R20 so as to be extinguished when tube VD is fired.

I claim:

1. Circuit arrangements comprising a plurality of cold cathode gas discharge tubes each having an anode, a cathode and an ignition electrode, means for simultaneously applying an ignition potential difference between the cathodes and corresponding ignition electrodes of at least two of said gas discharge tubes, an individual cathode load resistor for each of said gas discharge tubes, an individual anode load resistor for each of said gas discharge tubes, a common anode load resistor for all said gas discharge tubes, a source of high potential, means connecting said source of high potential to said common anode load resistor and connecting said common anode load resistor to all said individual anode load resistors and a resistance/ capacity circuit for each of said gas discharge tubes comprising a resistor and a capacitor in series and connected in parallel with the associated gas discharge tube and the cathode load resistor thereof, the resistor in each said resistance/ capacity circuit having such a value compared with the value of the individual anode load resistor that the reduction of anode potential resulting from one gas discharge tube igniting in response to an ignition potential difference applied simultaneously between the cathodes and ignition electrodes of at least two of the gas discharge tubes is not immediately efiective in reducing the anode potential applied to the second of the gas discharge tubes.

7 '2. Circuit arrangements as claimed in claim 1 and comprising in addition a thermionic tube having an anode, a cathode and at least one control grid electrode, the anode of said thermionic tube being connected to the junction of the individual and common anode load. resistors and means for applying a potential to an electrode other than the anode of said thermionic tube to cause the conduction of said thermionic tube whereby the anode potential applied to the gas discharge tubes is reduced and for maintaining said thermionic tube conducting for a period suflicient to enable any ignited gas discharge tube to be extinguished, due to the reduction in anode potential applied thereto.

Geohegan Mar. 3, 1953 Desch June 30, 1953 

